Depending on the type of radiation, and depending further on the specific radiation attribute to be monitored, a great variety of radiation sensors and detectors have been developed for electromagnetic as well as for particle radiation; see, e.g.,
R. J. Keyes, ed., Optical and Infrared Detectors, Springer-Verlag, 1977 and
E. Kowalski, Nuclear Electronics, Springer-Verlag, 1970.
Sensors and detectors are widely applicable as incorporated in a variety of devices for use in fields such as, e.g., instrumentation, communications, and robotics; with respect to robotics and related fields, position sensing applications are considered as particularly significant. Commercially available position-sensitive photodetectors are based on the photoelectric effect of the p-n junction, typically as implemented in the form of a silicon device. In this respect see, e.g.,
B. Schmidt et al., "Position-sensitive Photodetectors Made with Standard Silicon-planar Technology", Sensors and Actuators, Vol. 4 (1983), pp. 439-446.
P-n junction sensors are based on a physical phenomenon known as Wallmark effect or, more descriptively, as lateral photovoltaic effect; such effect consists in the appearance of a voltage parallel to a p-n junction when such junction is irradiated nonuniformly. For further detail and discussion of the lateral photovoltaic effect see, e.g.,
G. P. Petersson et al., "Position-sensitive Light Detectors with High Linearity", IEEE Journal of Solid-state Circuits, Vol. SC-13 (1978), pp. 392-399 and
H. Niu et al., "Application of Lateral Photovoltaic Effect to the Measurement of the Physical Quantities of P-N Junctions - Sheet Resistivity and Junction Conductance of H.sub.2.sup.+ -implanted Si", Japanese Journal of Applied Physics, Vol. 15 (1976), pp. 601-609.
While satisfactory p-n junction devices are readily made so long as their dimensions do not exceed a few micrometers, larger-size devices are difficult to make sufficiently uniform. Furthermore, when such devices are intended for position sensing, it has been found difficult to produce a voltage response which is sufficiently linear as a function of the position of a beam. Accordingly, there is demand for photodetectors and radiation sensors having an essentially linear response to the position of incident radiation.